no file sitemap.xml on the serveur

The file sitemap.xml or sitemap.xml.gz are industry standard. You wouldn’t want to change them.

Did you access domain.com/sitemap.xml? The file is created upon need/demand.

If it still isn’t created check that there is not a sitemap.xml file in the website’s root folder.

Hello,

I’m sitemaps tests
and even without changing it, I prefer to see it physically
However, in the folder, I have seen once
Moreover, I wanted it to be updated every post comments; there is more activity in comments that items

There is a physical sitemap file. It is located in /wp-content/sitemaps. There is a mapping from /sitemap.xml to the sitemap.xml located in /wp-content/sitemaps.

As for frequency pinging the bots on every comment will not help your site. Google and Bing determine when they want to crawl. Frequency is just a suggestion to them. If you visit Google Webmaster Tools for you site you’ll see their crawling activity.

I never found the file in the folder
so I have never been able to register with google webmaster

I preferred to simply remove it